This invention relates in general to vehicular brake systems, and in particular to control valves for electronically controlled vehicular brake systems.
Electronically controlled brake systems for vehicles are well known. A typical electronically controlled brake system includes a hydraulic control unit (HCU) connected in fluid communication between a master cylinder and a plurality of wheel brake assemblies. The HCU includes a housing containing control valves and other components such as a pump for selectively controlling pressure to the wheel brake assemblies.
The control valves are generally formed as electronically controlled solenoid valves. A typical solenoid valve includes a cylindrical armature slidably disposed in a tube or a sleeve for movement relative to a valve body. The armature may be biased in a fully open or closed position. The typical solenoid valve further includes a coil subassembly that generates a magnetic flux for moving the armature from the biased fully open position or closed position to a closed position or fully open position, respectively.
These types of control valves are generally used to control brake fluid pressure during non-base braking events, such as anti-lock, traction control, and vehicle stability control modes. However, because these types of valves are designed to operate generally in only the fully open and closed positions they do not provide “proportional” control characteristics desirable for controlling brake fluid pressure during base (“normal”) braking events. As such, these types of solenoid valves are generally not well suited for applications in which the brake fluid pressure is electronically controlled during base braking events.
Other types of prior art valves, such as spool valves, have been proposed which are capable of providing desirable proportional control characteristics for electronically controlling brake fluid pressure during base braking events. However, these types of valves are relatively expensive.
Accordingly there is a need for a control valve used in electronically controlled vehicular brake systems that is relatively inexpensive and provides for proportional control of brake fluid pressure during base braking events.